Method for setting a desired operating condition of a hybrid drive for a vehicle

ABSTRACT

A method is described for adjusting a setpoint operating state of a hybrid drive in a motor vehicle, the hybrid drive including an internal combustion engine and at least two electric motors as the drive motors, and the output shafts of the drive motor being capable of being operatively connected to a drive train of the vehicle, a setpoint operating point of the hybrid drive being adjusted as a function of an instantaneous power demand (output torque) on the hybrid drive and an instantaneous electrical power demand of an electrical system of the vehicle, by determining the speeds and the torques of the drive motors. 
     At least one of the electric motors ( 16 ) is controlled by voltage regulation and the other electric motor(s) ( 14 ) is/are controlled by speed regulation.

The present invention relates to a method for adjusting a setpointoperating state of a hybrid drive in a vehicle, the hybrid driveincluding an internal combustion engine and at least two electric motorsas the drive motors, and the output shafts of the drive motors beingcapable of being operatively connected to a drive train of the vehicle.

BACKGROUND INFORMATION

Hybrid drives for vehicles are known. In the case of the hybrid drivesdiscussed here, an internal combustion engine is combined with twoelectric motors, so that a plurality of drive sources is available tothe vehicle. In accordance with demands specified by a vehicle driver,the drive sources can selectively supply their input torques to a drivetrain of the vehicle. In a manner that is known per se, this results indifferent possible drive configurations depending on actual drivingsituations, the drive configurations serving in particular to enhancedriving comfort and reduce energy use while reducing pollutantemissions.

In the case of hybrid drives for vehicles, serial configurations,parallel configurations and mixed configurations of internal combustionengine and electric motors are known. Depending on the configuration,the electric motors are capable of being engaged directly or indirectlyin the drive train of the internal combustion engine. To operativelyconnect the internal combustion engine and/or the electric motors, it isknown to position them in such a manner that they are capable of beingoperatively connected to each other via gearing, e.g., planetary gearingor the like, and clutches.

To permit optimum implementation of a driver's request for drive powerfrom the hybrid drive, a coordinated actuation of the drive motors ofthe hybrid drive is required, which takes place in known fashion usingan “engine control unit.” The actuation of the drive motors can takeplace based on a setpoint operating state (optimum operating point) ofthe hybrid drive to be determined by the engine control unit.

It is known that, to determine the setpoint operating state, therequired power of the internal combustion engine, the required speed ofa first electric motor and the required torque of a second electricmotor must be determined based on a power demand on the hybrid drive,corresponding to a vehicle driver's desired torque, and based on aninstantaneous electrical power demand of an electrical system of thevehicle. These determined variables are sent to the drive motors assetpoint variables. It is disadvantageous here that the torque of thesecond electric motor cannot be adjusted with sufficient accuracy. Thisinstantaneous torque of the electric motor must therefore be estimatedbased on a measured phase current, for example. Due to this inexactestimation, the adjustment of the torque of the second electric motor isfaulty; as a result, the instantaneous output torque of the hybrid driveand the instantaneous power output of the vehicle electrical systemdeviate from their setpoint values. While the deviation of the outputtorque can be compensated for by a vehicle driver (by operating theaccelerator pedal or the like), the deviation of the output of thevehicle electrical system can only be detected and regulated indirectly.The vehicle system voltage is adjusted by a higher-order controller,which is only capable of operating slowly due to a high capacity of avehicle battery that is used. This regulation of the vehicle systemvoltage results in deviations of the instantaneous vehicle systemoutput, making it necessary to correct the setpoint operating point ofthe hybrid drive.

ADVANTAGES OF THE INVENTION

In contrast, the method according to the present invention having thefeatures stated in Claim 1 offers the advantage of enabling faster andeasier adjustment of the setpoint operating point of the hybrid drive.Due to the fact that one of the electric motors is controlled by voltageregulation and the other electric motor is controlled by speedregulation, it advantageously becomes possible to integrate theregulation of the vehicle system voltage directly into the adjustment ofthe setpoint operating point of the hybrid drive. This enables rapid andexact regulation of the vehicle system voltage. Since the vehicle systemvoltage is directly coupled to battery output, the battery output may bedetermined directly by performing a simple voltage measurement at theelectric motor. As a result, by regulating the voltage on the electricmotor, a simple regulation of the charging and/or discharging capacityof the battery is possible. In turn, this brings about the rapid andexact adjustment of the setpoint operating point of the hybrid drive.This further results in the advantage that a load on the vehicle batteryis reduced via the heretofore common regulation of the vehicle systemvoltage by a higher-order controller, so that the useful life of thevehicle battery is extended.

Further preferred embodiments of the present invention result from thefeatures stated in the subclaims.

DRAWINGS

The present invention is explained in greater detail hereinbelow in anexemplary embodiment, with reference to the attached drawing.

FIG. 1 shows a schematic view of a hybrid drive of a motor vehicle, and

FIG. 2 shows a block diagram of a method for adjusting a setpointoperating state of the hybrid drive.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

FIG. 1 is a schematic illustration of a hybrid drive of a motor vehiclelabelled in its entirety with numeral 10.

Hybrid drive 10 includes an internal combustion engine 12 and a firstelectric motor 14 and a second electric motor 16. A crankshaft 18 ofinternal combustion engine 12 and drive shafts 20 and 22 of electricmotors 14 and 16 are operatively connected to a gearing system 24. Driveshaft 20 is connected to a first planetary gearing 26, and drive shaft22 is connected to a second planetary gearing 28. A ring gear ofplanetary gearing 26 is connected to a manual transmission 30, and aring gear of planetary gearing 28 is connected to a manual transmission32. Manual transmissions 30 and 32 are in turn operatively connected toan output shaft 34 of gearing system 24. Output shaft 34 is operativelyconnected to a drive axle of the motor vehicle (not shown).

The design and mode of operation of a hybrid drive 10 of this nature aregenerally known, so they will not be discussed in further detail withinthe framework of the present description. In particular, via specificactuation of internal combustion engine 12 and/or electric motors 14 and16, a different input torque on output shaft 34 may be requested ofthem. This allows various operating modes of hybrid drive 10 to be set.Via actuation of a shifting mechanism, manual transmissions 30 and 32enable different gears to be engaged, in known fashion, the gears beinglabelled in this case as gears 1, 2, 3, 4, 5 and 6, and a reverse gearR. Electric motors 14 and 16 may also each be operated in generatoroperating mode and serve, e.g., to provide a vehicle system voltage forthe motor vehicle and to charge an accumulator (motor vehicle battery).Electric motors 14 and 16 are each associated with braking devices 36and 38, with which rotors of electric motors 14 and 16 may bemechanically braked.

FIG. 2 shows, in a block diagram, a section of a control unit foractuating hybrid drive 10, whereby the method according to the presentinvention for adjusting a setpoint operating state of hybrid drive 10will be discussed here in particular. It is clear that the control unitadditionally performs further open- and/or closed-loop controlfunctions.

The control unit includes a “coordinator” 40 for adjusting a setpointoperating point of hybrid drive 10. To this end, coordinator 40 receivesa signal 42 from a sensor 44, the signal specifying an instantaneouspower demand, i.e., an instantaneous output torque, on drive shaft 34.Sensor 44 is connected to an accelerator pedal, brake pedal, and/orcruise control of the motor vehicle, for example.

Coordinator 40 further receives a signal 46 from a vehicle electricalsystem 48 of the vehicle, which corresponds to the instantaneouselectric power demand of vehicle electrical system 48. Based on signals42 and 46 and, possibly, further signals that are not shown in thefigures, coordinator 40 determines setpoint variables for the drivemotors of hybrid drive 10, i.e., for internal combustion engine 12 andelectric motors 14 and 16. A first setpoint variable 50 that correspondsto a setpoint torque of internal combustion engine 12 is sent tointernal combustion engine 12. A second setpoint variable 52 thatcorresponds to a setpoint speed of electric motor 14 is sent to electricmotor 14. Electric motor 14 has a controller that sets this setpointspeed. Electric motor 14 delivers an actual signal 54 that correspondsto an actual speed of electric motor 14 to coordinator 40. Coordinator40 thereby detects when the permissible operating range has beenexceeded, and it is able to carry out an appropriate correction in theactuation of further assemblies.

By adjusting setpoint speed 52 of electric motor 14, a desired speed ofinternal combustion engine 12 is simultaneously set. Reference numeral64 indicates the current with which vehicle electrical system 48 ischarged or discharged by electric motor 14. Reference numeral 66indicates the current with which vehicle electrical system 48 is chargedor discharged by electric motor 16.

A further setpoint variable 56; e.g., the setpoint voltage, is suppliedto electric motor 16. Electric motor 16 adjusts the voltage in thevehicle electrical system based on setpoint variable 56.

Coordinator 40 selects setpoint variables 50, 52 and 56 in such a mannerthat the required output torque at output shaft 34 is realized, and therequired vehicle system output (signal 46) is made available. Therequired output torque is calculated based on vehicle speed and theinstantaneous power demand (signal 42). It is essential that the vehiclesystem voltage be coupled via the internal resistance of a vehiclebattery to the charging and/or discharging capacity of this battery.

The instantaneous vehicle system voltage is measured by a measurementsignal 58 and made available to the coordinator as signal 60.

Instead of measuring element 58, which measures the vehicle systemvoltage, a measuring element 58′ may alternatively be provided, whichmeasures the vehicle system voltage and a current flow in theintermediate voltage circuit between vehicle electrical system 48 andelectric motor 16 in combination. As a result, the vehicle system outputmay be determined directly and made available to coordinator 40 assignal 60′.

It becomes clear that integrating the regulation of the vehicle systemvoltage in coordinator 40 enables a rapid and exact regulation of thevehicle system voltage to adjust the setpoint operating point of hybriddrive 10. Torque-driven regulation of electric motor 16 is no longerrequired, thereby eliminating the sources of error associated therewith.

1. A method for adjusting a setpoint operating state of a hybrid drivein a vehicle, the hybrid drive having an internal combustion engine andat least two electric motors as drive motors, and the output shafts ofthe drive motor being operatively connectible to a drive train of thevehicle, a setpoint operating point of the hybrid drive being adjustedas a function of an instantaneous power demand (output torque) on thehybrid drive and an instantaneous electrical power demand of anelectrical system of the vehicle, by determining the speeds and thetorques of the drive motors, wherein at least one of the electric motors(16) is controlled by voltage regulation and the other electric motor(s)(14) is/are controlled by speed regulation.
 2. The method as recited inclaim 1, wherein the charging and/or discharging capacity of a batteryof the vehicle is adjusted by regulating the vehicle system voltage. 3.The method as recited in one of the preceding claims, wherein thevehicle electrical system capacity is determined directly by measuringthe vehicle system voltage and a current flow in the intermediatevoltage circuit between vehicle electrical system (48) and electricmotor (16).